The broad general goal of the proposed project is to apply stable isotope techniques to the study of intermediary metabolic processes in the pediatric age group. By infusions of appropriate substrates labelled with deuterium, carbon-13,-or nitrogen-15, and by subsequent isotopic analysis by combined gas chromatography-mass spectrometry, I plan to establish quantitative data for fuel homeostasis and fuel transport in normal infants and children. With this information, subsequent similar investigations in those children with disorders of fuel homeostasis may lead to an understanding of the pathogenic mechanisms underlying these dysfunctions.